Defibrillation electrode connection

ABSTRACT

A method for electrically attaching electrode wire to a conductor in a defibrillation lead is disclosed. The method comprises melting the end of the wire with a hydrogen torch to form a ball of metal, then crimping or welding the ball to the conductor or to a joining piece attached to the conductor. Also, a hydrogen torch (water welder) may be used to join two or more electrode wires to each other.

This is a continuation of application Ser. No. 08/126,291, filed on Sep.24, 1993, now U.S. Pat. No. 5,488,768.

FIELD OF THE INVENTION

This invention relates to medical electrical stimulation electrodes ingeneral and to implantable defibrillation electrodes in particular.

BACKGROUND OF THE INVENTION

It is well known that cardiac arrhythmias such as ventricularfibrillation may be controlled with devices such as implantabledefibrillators. Many different types of defibrillation electrodes havebeen suggested over the years, as can be seen from the followingexamples. In this discussion, no distinction will be made betweencardioversion and defibrillation; both will be referred to asdefibrillation.

U.S. Pat. No. 3,942,536 issued to Mirowski et al. discloses anintravascular bipolar catheter electrode system wherein each of twoelectrodes is composed of a plurality of spaced, low impedance rings. Asimplanted, the first electrode is located within the right ventricle(RV) and the second electrode is located in the superior vena cava(SVC).

In U.S. Pat. No. 4,161,952 issued to Kinney et al., a catheter electrodehas a coil of wound spring wire, with filler material beneath andbetween individual turns of coil such that only the outside of the woundwire is exposed to the patient's body. It is designed to reside in orabout the heart, as in the SVC or in the coronary sinus (CS).

U.S. Pat. No. 4,922,927 issued to Fine et al. teaches the use of tightlywound wire forming a tight coil on a support that is flared to provide agreater diameter along its midsection than at its ends, to form an RVelectrode. A copper-zirconium alloy wrapped with tantalum and coatedwith iridium oxide is suggested for the tightly wound wire.

Other types of transvenously placed leads are disclosed in U.S. Pat. No.4,998,975 issued to Cohen et al. One lead is placed through the heartwall, and into the pericardial space, and another is placedendocardially in a conventional manner. Both leads are shown withseveral embodiments, with the examples of general electrode constructionbeing to expose a section of the conductor coil, or to use ringelectrodes similar to those used in conventional bipolar pacemakerleads. Cohen et al. also describe two methods for steering more currentto a selected region of the heart. The first method is to apply variousvoltages to the connectors of each of four electrodes. The second methoduses the resistance of conductors, both between connector and electrode,and between two electrodes on the same lead, and the body tissueresistance between electrodes on different leads, to form a voltagedivider, thus creating a different potential at each electrode.

Another lead system patent, U.S. Pat. No. 5,007,436 issued to Smits,describes electrodes of both J and straight configurations, for use inthe RV, right atrium, great cardiac vein, or CS. The fabrication methodssuggested use close wound conductive coils mounted exterior to anelongated insulative sheath, or the method of Kinney et al.

Spiral shaped electrodes for endocardial, epicardial, orextrapericardial implantation are described in Heil, Jr. et al., U.S.Pat. No. 5,016,808, Fogarty et al., U.S. Pat. No. 4,860,769, and Hauseret al., U.S. Pat. No. 5,052,407. The electrodes of these patents usevarious construction techniques, including electrodeposition or vapordeposition onto a plastic tube, helically wound wire (round or ribbon,unifilar or multifilar, single or double helix) or conductive rings on aflexible insulating portion, and conductive screen wrapped around atubular body.

Other defibrillation leads are disclosed in Mehra et al., U.S. Pat. No.5,144,960, and in Bardy et al., U.S. Pat. No. 5,174,288.

Endotak SQ Model 0048 (Cardiac Pacemakers Inc., St. Paul, Minn., USA),described in "A Subcutaneous Lead Array for Implantable CardioverterDefibrillators" by Jordaens et al., published in PACE, Vol. 16, July1993, Part I, is an electrode system consisting of three conductiveelements that can be subcutaneously inserted. The conductive elements ofthis "array lead" are made of electrically common multifilar coil,joined in a silicone yoke, and separately introduced with a leadtunneler and peel-away sheaths.

Epicardial defibrillation leads typically are made of wire mesh, whichis welded in several places to another piece of mesh or foil, which isin turn crimped to a conductor. The mesh wire diameter is typically 0.10mm. The epicardial lead shown in Moore et al., U.S. Pat. No. 4,314,095,has an electrode connection formed by crimping a piece of wire mesh anda conductor into the channel of a U-shaped clip, then welding the meshportion to a wire mesh electrode. Ideker et al., in U.S. Pat. No.4,827,932, disclose a connection formed by spot welding a pair of tabsto both sides of a mesh electrode, then inserting the ends of the tabsand a coil conductor into a sleeve, then crimping the componentstogether.

Endocardial lead electrodes for pacing and defibrillation typically arejoined to conductors by crimps or welds. U.S. Pat. No. 4,662,382, issuedto Sleutz et al., describes such a connection made by crimping anelectrode wire and a conductor wire into a sleeve. A second electrodehas a hollow portion to accept a conductor coil and crimp pin, which getcrimped together. U.S. Pat. No. 4,784,161, issued to Skalsky et al.,describes a crimp connection having both an electrode wire and conductorwires wrapped around a shaft, with a crimp sleeve over both. In anotherembodiment, a bundle of electrode wires and a helical conductor have asupport pin through the middle of them; a crimp sleeve covers both theconductor and the bundled wires. U.S. Pat. Nos. 4,214,804 and 4,328,812, to Little and Ufford et al. respectively, disclose press fit, orswage fit, connections of ring electrodes to conductor coils. U.S. Pat.No. 4,161,952, to Kinney et al., teaches the use of metal connectingpieces to which is welded a 0.76 mm diameter electrode wire. Anelectrically conductive polymer such as silver-filled epoxy is used toelectrically connect the conductor to the metal connecting pieces.

As defibrillator technology improves and the demand for defibrillatorsincreases, it becomes increasingly desirable to have leads availablethat are easily implanted and capable of withstanding repeated flexingover a long period of time. In order to provide improved flexibility,prior art systems have begun to use very small wires which are fatigueresistant. This however presents a problem of making reliable electricalconnections. Crimps, swages, press fit connections, and the like requireat least some deformation of the parts being connected. In the case offine wires, say 0.08 mm diameter, it is very difficult to deform thewire to form a strong connection without weakening or breaking it. Thisis especially true considering that tolerances on crimp sleeves, crimppins, and crimp tool jaws can easily add up to more than the diameter ofthe wire being crimped. Welds require some melting of the material beingwelded. Resistance welds in particular require the application ofpressure. For fine wire, the wire may melt through or be crushed duringthe welding process. For fine coiled wire, neither crimping nor simplewelding is suitable because the wire needs to be unwound before pressureis applied, since flattening a fine coil will break it. On the otherhand, the coiled wire could become damaged by the process of unwindingit. Therefore, another method must be used to join these small wireelectrode elements to their lead conductors.

SUMMARY OF THE INVENTION

The present invention provides an electrode connection for a lead foruse with an implantable defibrillator system. In the preferredembodiment, small coils made of fine platinum iridium wire serve as theelectrode material. These fine wire electrodes are attached to the restof the lead by melting their ends into balls of metal with a hydrogentorch, and welding the balls to a sleeve to which a conductor isattached.

In an alternative embodiment, the connection is made by melting thesmall electrode coils into one large ball, then crimping the ball into asleeve to which a conductor is attached.

In a third embodiment, the ends of two or more electrode coils arejoined together by using a hydrogen torch to melt them into a ball.

It is thus an object of the present invention to provide an electricalconnection for wire electrodes for an implantable defibrillator.

It is another object of the invention to provide an electrode connectionthat is easily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present invention may be morereadily understood with reference to the following detailed descriptiontaken in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 illustrates a defibrillation electrode;

FIG. 2 is a detail view, partially cut away and partially in section, ofthe distal connection of the lead of FIG. 1;

FIG. 3 is a detail view of the distal end of the electrode coil of FIG.1;

FIG. 4 illustrates an alternative embodiment of the invention whichincludes a pacing electrode, and uses the electrode for bothdefibrillation and sensing;

FIG. 5 shows a sectional view of the distal end of the lead of FIG. 4;

FIG. 6 shows a detail view of the electrical connection of the lead ofFIG. 4;

FIG. 7 shows a cross sectional view of the proximal end of the electrodeof FIG. 4;

FIG. 8 illustrates one step in the manufacture of the lead of FIG. 4;

FIG. 9 shows a detail view of an electrode connection of a lead withseveral electrodes in parallel for subcutaneous implantation; and

FIG. 10 shows a patch electrode for epicardial or subcutaneousplacement.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a lead 18 having an electrode 20 electrically connected toa conductor coil 30 in two locations. The first connection 34 is at thedistal end of electrode 20, and the second connection 36 is at theproximal end. These connections can be welds, crimps, and the like, inany combination. The conductor coil 30 is in turn electrically connectedto connector 32 for coupling with a pulse generator such as the typedescribed in U.S. Pat. No. 5,007,422 to Pless et al., which is assignedto the assignee of the present application. The lead body diameter isgenerally about 2.5 to 4.5 mm. The lead is disclosed in U.S. Pat. No.5,439,485 to Mar et al. by Mar et al., for a "Flexible DefibrillationElectrode of Improved Construction" which is assigned to the assignee ofthe present application.

FIG. 2 shows a detail view of the distal connection of the lead 18 ofFIG. 1. Electrode 20 is shown to be constructed of many (six) electrodecoils 24 helically wound around a flexible tubular supporting core 22,which may be either electrically conductive or insulative, and may beextruded or molded. This structure has elastomeric material 28, whichalso may be conductive or insulative, partially encapsulating theelectrode coils. The many electrode coils increase conductivity andredundancy. One method of achieving this structure is to completelyencapsulate the wrapped electrode coils, then abrade away the surface topartially expose the coils using the method of Mar et al., U.S. Pat. No.5,226,260, which is assigned to the assignee of the present applicationand which is incorporated herein by reference. A conductor 30 extendsthrough the lumen of core 22, making connection 34 at the distal end ofelectrode 20. Conductor 30 is crimped to a sleeve 31 and to a pin 33. Inaccordance with this invention, the distal ends of electrode coils 24are melted into balls 27, which are then welded to sleeve 31, forming anelectrical connection to the conductor coil. The connection 34 is thencovered by a protective cap 35, which may be electrically conductive orinsulative. Protective cap 35 seals the electrode connection from bodyfluids. Conductor coil 30 forms an inner lumen 38 through which a styletmay be placed to stiffen the lead during implantation. Pin 33 servesboth as a support for coil 30 and sleeve 31 for crimping, and as a stopfor the stylet.

FIG. 3 shows that each electrode coil 24 is made from a helically woundmetal wire 26, which may be round or flat in cross section. This wiremust be very strong, fatigue resistant, conductive, corrosion resistant,and biocompatible. Platinum iridium is one example of such a material.Electrode coil 24 is shown without an inner core; however, a thin wireor plastic filament could be located within coil 24 to provide eitherincreased electrical conductivity, mechanical redundancy, or both. Thefilament could be metal or nylon, for example. In order for the lead tobe sufficiently thin to be transvenously implantable, electrode coils 24should be between about 0.2 and 0.4 mm, and wire 26 should be about 0.05to 0.10 mm in diameter. Close winding of wire 26 into electrode coils 24provides more exposed metal for charge transfer to tissue. However,space winding decreases the lengths of wire in the coils, decreasing endto end electrode resistance. Additionally, space winding provides moresurface for matrix material to mechanically stabilize coils and allowsfor a substantial volume of matrix material that can flex with the heartand body motion instead of pulling away from the coils. Therefore, acertain amount of space is preferred, typically one-half to one wirediameter space between wires. Similarly, electrode coils 24 can be closeor space wound onto core 22. The same general principles apply.

The distal end of each electrode coil 24 is melted into a ball 27, whichprovides more volume of material to form a strong and reliable crimp orweld. This melted ball structure works particularly well when made of anoble material such as a platinum iridium alloy. A hydrogen torch, alsocalled a "water welder", is one suitable means for melting the coil toform the ball. This device dissociates water into hydrogen and oxygen,then burns the hydrogen to form water again. This process burns cleanly,without incorporating byproducts into the melting coil, which isimportant for maintaining biocompatibility and material consistency forany subsequent welding.

FIG. 4 shows a lead 18' with a pacing electrode 44, and electrode 20which is used alternately for defibrillation and for sensing. Pacingelectrode 44 may be of any of the numerous constructions known in theart. A fixation mechanism 45 is shown as tines, but may be any known inthe art, including a screw used for both pacing and fixation. Pacingelectrode 44 is electrically connected to a pacing conductor coil 40,which is in turn connected to a pacing connector 43. Electrode 20 iselectrically connected to conductor coil 30, which is in turnelectrically connected to both defibrillation connector 32 and a sensingconnector ring 39.

FIG. 5 shows a detail view of the distal end of the lead of FIG. 4.Electrode 20 is shown to be constructed of a plurality of electrodecoils 24 helically wound around flexible tubular supporting core 22.This structure has elastomeric material 28 partially encapsulating theelectrode coils. Conductor 30 extends through the lumen of core 22,making connection 34 at the distal end of electrode 20. Conductor 30 iswelded to the face of sleeve 29, as described in U.S. Pat. No. 5,385,578to Bush et al., for an "Electrical Connection for Medical ElectricalStimulation Electrodes" which is assigned to the assignee of the presentapplication and which is incorporated herein by reference. The distalends of electrode coils 24 are melted into balls 27, and are then weldedto sleeve 29, forming electrical connection 34 to the conductor coil. Apacing conductor coil 40 extends through the lumen of tubular core 22and is electrically insulated from conductor coil 30 by an insulator 42.Pacing conductor coil 40 is shown connected by a crimp connection topacing electrode 44 and a crimp pin 41; this connection mayalternatively be a weld.

FIG. 6 shows a detail view of electrical connection 34. The distal endof conductor coil 30 has been welded to the face of sleeve 29. Electrodecoils 24 have had their distal ends melted into balls 27, then welded tothe outside surface of sleeve 29. Alternatively, the balls 27 could havebeen connected directly to the conductor coil 30.

FIG. 7 shows a cross sectional view of the proximal end of electrode 20.Two groups of electrode coils 24 have their proximal ends melted intoballs 27' to provide electrical redundancy. Molded electrode core tube22 has two pockets 25 in its proximal end into which balls 27' areplaced prior to wrapping electrode coils 24 onto tube 22. Afterelastomeric material 28 is applied, an electrical insulation 37 isjoined to electrode 20 using a joining material 47, for example siliconerubber. A mandrel is used to keep the lumen open during this process, sothat the conductor can be passed through the joint and connected at thedistal end of electrode 20.

FIG. 8 shows one group of three electrode coils 24 with proximal endsmelted into ball 27'. This group of three electrode coils can be woundonto a tube such as core tube 22 of FIG. 7 in several ways. Thepreferred method is to insert a mandrel into a molded core tube, placethe mandrel into a lathe-type coil winder, insert one group of threeelectrode coils 24 into each of two pockets of the tube, then use thecoil winder to wind the electrode coils 24 around the tube. After theelectrode coils 24 are wound onto the core tube, elastomeric materialmay be compression molded over the coils and core. An alternative methodis to embed electrode coils 24 into uncured elastomeric material thathas been rolled into thin strips, then wrap the coil embedded strips ofelastomeric material around a core tube, then cure the elastomericmaterial. A third alternative is to apply uncured elastomeric materialto a cured core, then wind electrode coils 24 about the core, embeddingthem into the elastomeric material. Yet a fourth alternative is tomanufacture the core and elastomeric material portion simultaneously byputting uncured rubber onto a mandrel to form both portions; electrodecoils 24 are then embedded into the surface of the rubber, and therubber is cured.

FIG. 9 illustrates a lead with three electrodes 20, intended forimplantation subcutaneously on the left lateral part of the chest. Theyare of the same polarity, and are connected to a common node onconductor 30. Electrode coils 24 are connected at distal ends by meltedballs 27' and wound onto flexible cores 48. Flexible embedding material50 partially covers electrode coils 24. The proximal ends of electrodecoils 24 are all connected by melting them into ball 27". Ball 27" iscrimped into metal joining piece 58. Also crimped to metal joining piece58 is crimp sleeve 31 and conductor coil 30. A protective strain reliefmolding 60 encapsulates the entire connection.

FIG. 10 illustrates a lead with one patch electrode 61, having aplurality of electrode coils 62 partially embedded in a silicone rubbersurface 64. The electrode coils are of the same polarity, and areconnected to a common node on conductor 30. Electrode coils 62 areconnected by melting both ends of all of them into ball 27". Ball 27" iscrimped into metal joining piece 58. Also crimped to metal joining piece58 is crimp sleeve 31 and conductor coil 30. Alternatively, ball 27"could have been connected directly to conductor 30. A protective strainrelief molding 60 encapsulates the entire connection.

Because the electrode coil wire is longer and thinner than the electrodeelements of the prior art, the electrode of the present invention can bemade with a certain amount of resistance along its length, say, 3 to 15ohms. This property of the electrode can be used to directdefibrillation energy to selected regions of the heart by careful choiceof connection locations of electrode to conductor. For example, if theelectrode 20 of FIG. 4 were placed with its distal end in the apex ofthe RV, current would be steered to the RV apex since that is where theconductor attaches to the electrode at connection 34. On the other hand,because of the electrode connections 34 and 36 on either end ofelectrode 20 of FIG. 1, the current distribution would be more evenalong the electrode length than in the electrode of FIG. 4, since thepotential is the same at either end, assuming a very low resistanceconductor 30. In this case, the end to end electrode resistance is alsoreduced, with the highest resistance being in the middle of theelectrode. The connection could also be made in the middle of theelectrode, instead of or in addition to the ends. With the electrodeconnected to the conductor in only the middle of the electrode and notthe ends, current density would be more even since end effects would bereduced. Several connections between the conductor and the electrode maybe made along the length of one electrode. This is desirable forreducing overall resistance, particularly when the electrode is long.

The above has been offered for illustrative purposes only and is notintended to limit the scope of the invention of this application, whichis as defined in the claims below.

That which is claimed is:
 1. An electrical connection comprising:one endof each of a plurality of coiled platinum iridium wires melted to form aball of metal such that each of said coiled platinum iridium wires isattached to said ball, said ball crimped within or welded to a metalsleeve, and said sleeve electrically attached to a conductor.
 2. Anelectrical connection produced by the steps of:melting one end of eachof a plurality of coiled platinum iridium wires to form a ball of metalsuch that each of said coiled platinum iridium wires is attached to saidball; crimping or welding said ball to a metal sleeve; and electricallyattaching said metal sleeve to a conductor.
 3. An electrical connectioncomprising:one end of each of a plurality of coiled platinum iridiumwires melted to form a ball of metal such that each of said coiledplatinum iridium wires is attached to said ball, and said ball connectedto a conductor.
 4. An electrical connection produced by the stepsof:melting one end of each of a plurality of coiled platinum iridiumwires to form a ball of metal such that each of said coiled platinumiridium wires is attached to said ball; and connecting said ball to aconductor.